Cost effective structures having desirable stiffness are needed. Foam sandwich constructions and methods for generating them are known in the art. The construction includes a central foam layer which is formed of material selected so that central layer can be a substantially thick spacer contributing to the overall stiffness of the construction. The materials for the skins primarily are glass fiber reinforced plastic. The core materials generally are polyurethane foam. But it is possible to use other materials for both. Planar sandwich constructions such as straight beams or flat panels are included. The invention may also find use in relation to curved constructions, such as hulls of boats or tubs.
The invention can be applied to 2-, 3- (and more) layer sheet-like structures, such as films, walls and other types of ‘physical barriers’, ranging from flexible to rigid, whereby the unlimited range of the individual layer thicknesses, their moduli as well as the costs can be used as input parameters.